The ornamental design for a rotor, as shown and described.
FIG. 1 is a top plan view of a rotor according to the present teachings, wherein the bottom plan view is identical to the top plan view;
FIG. 2 is a top perspective view thereof;
FIG. 3 is a side view thereof; and,
FIG. 4 is shows an enlarged portion of the rotor described by area 4—4 in FIG. 1.
The broken lines in the drawing depict unclaimed environmental subject matter with the exception of the broken lines surrounding the enlarged portion of the design in FIGS. 1 and 4 that depict the area of enlargement; none of the broken lines are included in the claimed design.